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Awash in Artificial Light, the World Gets 2 Percent Brighter Each Year

Making outdoor lighting more efficient doesn't reduce light pollution—it encourages people to use more light

3 min read
An animated gif shows changes in outdoor lighting in Calgary, Alberta, Canada as seen from the International Space Station in 2010 and 2015.
These photos from 2010 and 2015 show changes in outdoor lighting in Calgary, Canada. In the 2015 photo, many new areas on the edge of Calgary are lit up. Some neighborhoods have also switched from orange sodium lamps to white LED lamps.
Gif: Earth Science and Remote Sensing Unit/Johnson Space Center/NASA

Around the world, more lights keep being switched on. A new analysis of satellite data from the past four years shows that the total acreage lit by artificial light at night increased by an average of 2.2 percent a year. The brightness of the areas lit at the start of the study also increased by the same rate—2.2 percent annually—around the globe.

That growth is disappointing, says Christopher Kyba of the GFZ German Research Center for Geoscience in Potsdam. A member of the International Dark-Sky Association, he had hoped that efforts to switch outdoor lighting from sodium lamps to efficient LEDs would reverse the loss of the night.

Instead, he says, "the use of artificial lighting is increasing and we're losing more and more of the night on a planetary scale."

Light pollution was an issue even before LEDs, and it wasn't just astronomers who complained. City-dwellers were annoyed by the glare from bright lights shining in their windows. Naturalists found that artificial lights were affecting animals including insects, bats, and sea turtles. In 2012, the European Union launched the Loss of the Night Network to monitor environmental effects of outdoor lighting.

The improvements in energy efficiency brought by LED street lights are clear. But the extent of artificial lighting at night has been hard to monitor. Photos from military weather satellite photos showed the global extent of artificial lighting, but the cameras were not calibrated to measure brightness and were prone to changes in sensitivity.

That changed after the October 2011 launch of a NOAA satellite carrying the Visible Infrared Imaging Radiometer Suite—a set of instruments that includes a sensor calibrated to measure nighttime radiance at wavelengths from 500 to 900 nanometers. That sensor's main purpose is to gather data for short-term weather forecasts and to monitor disaster zones. But analysis of that well-calibrated data also can measure changes in the brightness and extent of artificial lighting at night.
 

Chart reflecting changes in artificially lit surface of Earth at night.Most of the world is getting brighter, even when measured by instruments that do not account for the blue component of outdoor LED lighting. The few exceptions include countries with ongoing wars.Image: Carla Schaffer/AAAS

Using data collected from 2012 to 2016, Kyba's group found that night-time lighting increased in brightness and area across most of Africa, Asia, and South America. Levels remained stable in some countries that already were bright, such as the United States and the Netherlands, they report in Science Advances.

Yet the satellite data understates the actual increase because its sensor cannot detect blue light, which is at the center of an ongoing controversy over the environmental impact of LED street lights.

LED street lamps are built around bright blue LEDs, which excite yellow phosphors to produce a blend of colors that looks white to the eye. LED lamps can be designed to block blue, but highway engineers prefer blue-rich LEDs because human night vision is more sensitive in that range. Up to half of an LED lamp's output can fall in the blue region missed by the sensor.

'The use of artificial lighting is increasing and we're losing more and more of the night on a planetary scale.'

Because the sensor misses blue light, Kyba says it recorded a decrease in light from Milan and other cities which switched from old sodium lamps to LEDs during the measurements. Pinning down the real change in brightness will require a different sensor that is sensitive across the visible spectrum and calibrated to match human vision.

Thus, although LED lighting has saved energy, people have been turning on more lights rather than pocketing their savings. It's called the rebound effect, and it's been going on for centuries, write Kyba and his colleagues: "Regardless of historical or geographical context, humans tend to use as much artificial light as they can buy for about 0.7 percent of [gross domestic product]."

The Conversation (0)
This photograph shows a car with the words “We Drive Solar” on the door, connected to a charging station. A windmill can be seen in the background.

The Dutch city of Utrecht is embracing vehicle-to-grid technology, an example of which is shown here—an EV connected to a bidirectional charger. The historic Rijn en Zon windmill provides a fitting background for this scene.

We Drive Solar

Hundreds of charging stations for electric vehicles dot Utrecht’s urban landscape in the Netherlands like little electric mushrooms. Unlike those you may have grown accustomed to seeing, many of these stations don’t just charge electric cars—they can also send power from vehicle batteries to the local utility grid for use by homes and businesses.

Debates over the feasibility and value of such vehicle-to-grid technology go back decades. Those arguments are not yet settled. But big automakers like Volkswagen, Nissan, and Hyundai have moved to produce the kinds of cars that can use such bidirectional chargers—alongside similar vehicle-to-home technology, whereby your car can power your house, say, during a blackout, as promoted by Ford with its new F-150 Lightning. Given the rapid uptake of electric vehicles, many people are thinking hard about how to make the best use of all that rolling battery power.

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